This invention relates to a ground anchor especially but not exclusively for securing objects to the seabed. One instance of particular interest is the anchoring of subsea mattresses, especially viscous curtain artificial seaweed mattresses, which have to resist substantial drag forces induced by wave and current action.
A known design of ground anchor comprises an anchor plate to be driven edge first into the ground, a flexible anchor strap or web attached to the plate, the plate including a projecting tail flap and a socket or other means for receiving an end of a driving tool. In use, the plate is driven substantially vertically into the ground and when it is at the desired depth, the driving tool is withdrawn and a load is applied to the anchor strap which causes the anchor plate to pivot about the trailing flap into a skew position (and ultimately a generally horizontal position) in which it affords good anchoring. Ground anchors of this sort are shown, for example, in French patent specification no. 2470823 and European patent specification no. 0169872A.
In the anchor of the above French specification, the tail flap projects laterally of the anchor plate and so causes the formation of an entry channel in the ground which is wide in relation to the anchor plate. As a result, there is a risk of the anchor being pulled some distance back up the channel when a load is applied to the anchor strap. With a view to overcoming this and other problems, the anchor of European patent specification no. 0169872A has a hinged tail flap which can be oriented to two different angular dispositions relative to the anchor plate. The flap is maintained in the first position, at a low angle to the anchor plate, whilst the anchor is driven into the ground, but is then moved to a second position inclined at a greater angle to the plate when the driving tool is withdrawn. However, whilst this arrangement can overcome the disadvantage of the French specification anchor, it does itself suffer from the fact that it is difficult to give adequate strength to the hinged tail flap to withstand the substantial forces which can arise as load is applied to the anchor strap to turn the buried anchor into the skew position.
We have now found that by a modification in the known design of ground anchors described above, a more efficient operation of the anchor can be achieved without the various disadvantages noted above.